1. Trypsinogen (inactive)- activated by intestinal endopeptidase to trypsin2. Chymotrypsinogen (inactive) stimulated by trypsin to form chymotrypsin which acts next3. Procarboxypeptidase (inactive)- stimulated by trypsin to form carboxypeptidase which acts last

Result of protein in small intestine after 3 pancreatic enzymes have acted

mixture of small peptides and polypeptides

Order of intestinal enzymes acting on mixture of small peptides and polypeptides in small intestine

1. Aminopeptidase: lops off amino acid at amino end

2. Carboxypeptidase: lops off amino acid at carboxyl end

3. Dipeptidase: breaks down larger peptides

Final result of proteins after small intestine digestion is complete

free amino acids (some possible dipeptides + tripeptides)

these are water soluble and ready to be absorbed into the hepatic portal system

Fat Digestion

true fats (triglycerides- made of glycerol + 3 fatty acids attached)

only enzyme is pancreatic lipase which acts in the small intestine (takes triglycerides and breaks them down to glycerol + fatty acids +monoglycerides)

end products: glycerol and small faty acids (water soluble- absorbed into HPS) other fatty acids and monoglycerides need to go into lymph first, but are not water soluble right now so can't be taken up by intestinal cells to go to lymph

Continuation of digestion for larger fatty acids and monoglycerides

3. bile salts form micelles making remaining fats soluble so intestinal cells can take them up

4. intestinal cells absorb these but then in intestines, products go back together to form triglycerides and aren't water soluble anymore and they need to be to go to the lymph and blood

5. Chylomicrons form in intestine to go to the lacteals of small intestine to lymphatics to the thoracic duct to the venous blood to the cells, but now they have to get into the tissues

6. In the tissues, capillaries have lipase to breakdown triglycerides to fatty acid and glycerol which will go into the cells

free amino acids: absorbed by active transport with a carrier based on amino acid structure

in a newborn: whole protein (large) absorbed through endocytosis

Fat Absorption

fatty acids and monoglycerides: absorbed in small intestine into lymph by diffusion

glycerol + small fatty acids: absorbed by diffusion into the blood

Nucleic Acid absorption

products of digestion absorbed by active transport

water: absorbed by osmosis

vitamins: some dissolve in fats (A,E,D,K)- absorbed through diffusion and follow the other fats into the lymph; others are water soluble (all B + C vitamins)absorbed through diffusion or active trasport

stimulus: partially digested food but the food is now going into the duodenum of the small intestine- this triggers intestinal gastrin (hormon made by small intestine) which stimulates stomach to have increased secretions and increased contraction to churn the food.

Inhibitory effects on the stomach (Nervous and Endocrine systems)

both nervous and hormonal: stimulus is chime in the duodenum, but esp if theres a large amount to cause physical distention of the duodenum, or especially if fat is in chime

vagus nerve is inhibited- slowing stomach digestion

fatty chime stimulates enterogastrons

enterogastrons

hormones that have an inhibitory effect on the stomach

includes several hormones like choleycistokinin and seretin

these hormones decrease the force of contraction of the pylorus region (closest to small intestine) of the stomach and decreases gastric secretions emptying into small intestine. This allows time for digestion (esp of fat- bile and lipase) in the small intestine

Why do fatty foods keep us fuller longer

food with fat stays in the stomach longer than food without fat because it takes longer to digest

Regulation of Digestion by Nervous and Endocrine Systems: Bile and Pancreatic Secretions

2 hormones in the small intestine that affect both bile and pancreatic secretions

--> Choleycystikinin (CCK)

--> Secretin

both of these are stimulated by acidic fatty chime

they are both synergistic- they enhance each other

Cholecystikinin

Effect on bile: stimulates gall bladder to contract and release the bile into the cystic duct which goes to the small intestine

Effect on pancreas: stimulates pancreas to increase secretions esp rich in enzymes including lipase to break down fat (the more food with fat the more bile you will need and the more lipase to digest it)

Secretin

stimulates the liver to make the bile

stimulates pancrease to release a lot of bicarbonate to the small intestine to neutralize acids

Vagas nerve relation to bile and pancreatic secretions

stimulates gall bladder contraction to secrete bile

stimulates release of pancreatic secretions

Regulation of Digestion by Nervous and Endocrine systems: Small Intestine

control of smooth muscle contraction, motility of small intestine by the nervous system and hormones

stimulus: the distention of small intestine by partially digested food; there will be a nervous reflex (vagus nerve)

if you haven't eaten: low intestinal volume stimulates motilin (hormone made in sm. intestine) which stimulates parastolsys (wave like gentler contraction) of small intestine which moves along bacteria sloughed off cells, etc, until next meal

Defecation

the release of feces from the rectum (last part of the large intestine) out the anus (opening)

large intestine has normal flora bacteria that make some vitamins that we absorb (Vitamin K and some B vitamins)